The nonionic surfactants known in the art and used widely include glycerol fatty acid esters, sorbitan fatty acid esters, poly(oxyethylene)sorbitan fatty acid esters, poly(oxyethylene) fatty acid esters, poly(oxyethylene)alkyl ethers, poly(oxyethylene)alkyl phenyl ethers, hydrogenated castor oil poly(oxyethylene) adducts and the like. These surfactants are generally broken down into lipophilic and hydrophilic types, the former having no poly(oxyethylene)chain or a short poly(oxyethylene)chain and the latter having a long poly(oxyethylene)chain. A surfactant mixture containing a higher proportion of hydrophilic surfactants provides a oil-in-water (O/W) type emulsion having its hydrophilic-lipophilic balance (HLB) adjusted to 10-15, while a surfactant mixture containing a higher proportion of hydrophilic surfactants provides a water-in-oil (W/O) type emulsion having its HLB adjusted to 4-6. Thus sophisticated adjustment of the hydrophilic-lipophilic balance is required for the preparation of stable emulsions. With the nonionic surface active agents, that adjustment is performed making use of the poly(oxyethylene)chain. This is because the control of the chain length of ethylene oxide is easy and can meet sufficiently the requirement on sophisticated HLB. However, the surfactants to which ethylene oxide is added have some disadvantages in that dioxane forms during synthesis, they suffer oxidation with the lapse of time so that elution of formaldehyde takes place and their pH shifts toward acidity. These problems may be solved by the addition of antioxidants; however, the use of such antioxidants is unpreferable in view of safety.
On the other hand, the nonionic surfactants known in the art and used extensively as solubilizers include poly(oxyethylene)octyl phenyl ether, poly(oxyethylene)nonyl phenyl ether, poly(oxyethylene)oleyl ether, poly(oxyethylene)monolaurate, poly(oxyethylene)monooleate, hydrogenated castor oil poly(oxyethylene)adducts, poly(oxypropylene) poly(oxyethylene)cetyl ether, poly(oxyethylene)2-hexyldecyl ether and the like. All of these solubilizers are Micelle-dissoolved in water, and are so adjusted that the resulting aqueous solutions are put into a relatively hydrophilic state having a HLB of not less than 12 so as to solubilize oily matters, perfumes, oil-soluble matters, etc. To this end, ethylene oxide is unexceptionally added to these solubilizers. Like the foregoing emulsifiers, however, the aqueous solution of surfactants to which ethylene oxide is added causes elution of formaldehyde and its pH shifts toward acidity, since the chain of ethylene oxide undergoes oxidation with the lapse of time. To this end, antioxidants or buffer solutions are added for pH adjustment. However, there is an increasing demand for solubilizers substantially insensitive to oxidation in view of both safety and the stability of products. To add to this, the conventional solubilizers generally have so long a defoaming time that, when they are applied over the inside of a container or the skin, there are still some bubbles remaining on the surface thereof, which pose problems in connection with appearance and touch.
The aforesaid emulsifiers and solubilizers share a common problem. Antiseptics now used with cosmetics include paraben compounds such as methylparaben, which are known to be adsorbed onto the ethylene oxide moieties of surfactants and hence less effective.
U.S. Pat. No. 3,846,546, West German Pat. No. 1 719 434 and French Pat. No. 1 553 145 specifications disclose emulsifiers that are related to compounds of the present invention. However, since these known emulsifiers are of the branched structure that 1, 2 bonding is present in the alkylene oxide group, the following disadvantages are found from the standpoint of synthesis; (1) an alcohol used as a starting material remains unreacted, (2) the distribution of molecular weight is wide, (3) an addition reaction does not proceed so that difficulties are encountered in making them hydrophilic, (4) the content of polyglycerol unbonded to the starting alcohol is high, etc. In view of their physical properties, the known emulsifiers are also disadvantageous in that they are poor in solubility in water and dispersibility in O/W emulsions so that they do not function as good solubilizers and emulsifiers for O/W emulsions. This holds for even the compounds of these emulsifiers having an increased number of moles of hydrophilic groups present.